House Oversight Committee Chairman Jason Chaffetz (R-Utah) won't run for office in 2018. Here's a look back at the rocky year Chaffetz has had since Trump took office. (Jenny Starrs/The Washington Post)

Update: Chaffetz is now suggesting he may not finish out his term -- perhaps further evidence of the thanklessness of his day job and how unproductive it is to his political future.

Rep. Jason Chaffetz's retirement announcement Wednesday came as a surprise. Talk quickly turned to whether it was because liberals successfully berated him at town hall meetings, whether he feared a well-funded opponent in 2018, and/or whether he was just trying to get a head start on the 2020 Utah governor's race.

The last of these makes complete sense, as The Fix's Amber Phillips notes. But the first feeds into an emerging reality of 2017: Trump is giving the people charged with investigating him fits.

Because Republicans are in the majority, those people happen to be fellow Republicans. And that's creating some impossible choices.

Through Trump's reluctance to quash potential conflicts of interest and his penchant for making wild accusations and then pawning them off on investigators, jobs such as Chaffetz's House Oversight Committee chairmanship have become completely thankless. Less than three months into the Trump administration, Chaffetz was forced to repeatedly shrug off Democrats and watchdogs' calls for him to investigate Trump's possible conflicts of interest. He also had to answer for Trump's allegation that millions of people voted illegally in the 2016 election. He was even pressed to investigate Nunes's conduct, which led the House Intelligence Committee chairman to hand off his Russia investigation.

Even before Chaffetz announced his abrupt exit, his political luck had suffered a steep decline when Trump was elected. As oversight chairman, he was preparing to spend four years investigating President Hillary Clinton’s alleged scandals and misdeeds. Then the Republicans unexpectedly seized control of the White House, leaving Chaffetz with the unenviable task of policing his own party. It was a fraught job to begin with, and his casual attitude toward the Trump family’s potential conflicts of interest — demonstrated in his interview with melast month — has only increased the pressure on him.

“Aside from Trump and Clinton,” one Utah Republican told me last month, “nobody’s fortunes changed more on presidential election night than Jason Chaffetz.”

It's one thing to shrug off clearly partisan efforts to get you to investigate a president, and most presidents are careful to avoid doing the kinds of things that put you in that position. But Trump has no such compunction. He's not afraid to saddle you with investigating his wild, evidence-free claims. And not only that; he will gladly take you on publicly if you run afoul of him.

For Chaffetz and Nunes, that leads to decisions between giving in to extraordinary — and in many cases, legitimate — public pressure to investigate Trump and doing what your president and party want you to.

Nunes erred way too much toward the latter and paid the price. And you can bet an ambitious and smart politician like Chaffetz knows this whole thing is a lose-lose situation for him.